The invention relates to a brake booster of tandem type having a pair of front and rear power pistons disposed seriatim within an enclosed shell.
A conventional brake booster of tandem type includes an enclosed shell formed by a front and a rear shell, and the interior of the shell is divided by a center plate into a pair of chambers. A chamber which is located forwardly of the center plate is in turn divided by a combination of a front power piston and a front diaphragm into another pair of chambers, and a chamber disposed rearwardly of the center plate is also divided by a combination of a rear power piston and a rear diaphragm into a pair of chambers.
A valve body internally housing a valve mechanism which opens and closes fluid passages slidably fits in a central portion of the center plate with a seal member interposed therebetween, and the inner periphery of the front and rear power pistons and diaphragms are secured respectively to the outer periphery of the valve body on the opposite sides of the center plate.
A pair of passages are formed within the valve body, one passage provides a communication between the constant pressure chambers which are located forwardly of the front and rear diaphragms in communication with a source of negative pressure, and another passage providing a communication between variable pressure chambers both disposed rearwardly of the respective diaphragms.
In a conventional arrangement as described above, the area through which the valve body slides with respect to the center plate and the area where the front diaphragm and the front power piston are clamped to the valve body are disposed seriatim axially, so that it results the booster to be suffered from an increased overall length. In addition, the passage which provides a communication between the both variable pressure chambers is located in a region of the valve body where the strength is of a greater significance, and this prevented an increased channel area from being obtained.
In a conventional brake booster of tandem type, when assembling the valve body and the center body together, it is essential to assure a positive communication between portions of passages which provide a communication between pressure chambers. The respective passage portions must be positioned to provide a communication therebetween while rotating the both bodies, which prevented an efficient assembly from being achieved.